1. Field of the Invention
The invention relates to a material feed device for an extruder, comprising a more particularly funnel-shaped storage container acting as a weighing container of a mass throughput weighing device and suspended with provision for free movement from measuring members and discharging via a tubular outlet into the inlet of a feed unit of the extruder, more particularly a cylinder containing a feed screw, the outlet and inlet being sealed off from outside by a seal which enables the storage tank to move freely.
2. Discussion of Prior Art
In a prior art material feed device of the kind specified the seal takes the form of bellows connected by one edge to the inlet of the feed unit and by the other edge to the outlet of the storage container. The seal bridges an axial gap between the outlet and inlet and enables the storage container with its outlet to move freely both vertically and horizontally in relation to the feed unit disposed stationary with its inlet. Such freedom of movement is necessary, since otherwise it is impossible for the weighing device to deal continuously with the mass throughput.
However, the use of material feed device of the kind specified has shown that the mass throughput is not dealt with satisfactorily. It was found that one source of error was the flexible bellows-type seal. To perform its sealing function, the seal cannot be infinitely flexible, but requires some rigidity. The seal limits more particularly horizontal mobility, but such mobility is necessary, since if the measuring members used are, for example, bending rods, the weighing container inevitably makes horizontal movements.